An embodiment of the invention is directed to a high-voltage device comprising an internal measuring resistor. The field of the invention is related to generation of high voltages and instruments or an apparatus using these high voltages. In particular, the field of the invention is directed to medical apparatuses for the acquisition of radiological images such as X-ray images.
In the prior art, generation of X-rays for medical image acquisition requires a power supply voltage, between the anode and the cathode of the X-ray tube, ranging from 40 kV (kilo-volts) to more than 160 kV. This voltage is generally obtained with a bipolar device that applies two high voltages that are symmetrical relative to ground. In other words, to have 160 kV between the anode and the cathode, a device that generates +80 kV at the anode and −80 kV at the cathode is used. Controlling the sum of the two high voltages, namely the positive and negative high voltages, applied to the anode and the cathode, generally regulates this high voltage. Two identical devices that divide the voltage measured in a ratio of about 10,000, which is generally 1V for 10 kV, measure the two high voltages. To work well in oil at voltages of about 100 kilo-volts, a measurement device of this kind must have a maximum spacing between two conductive plates of about 40 mm (millimeter).
However, considerations of X-ray image quality have led to the connecting of the anode to the envelope of the tube which is itself ground-connected and to the application of all the voltage to the cathode alone. The power supply for the tube is no longer a bipolar (+ and −80 kV) supply but a one-pole (−160 kV) supply. The high-voltage generator now delivers only one voltage that, however, is twice the value of the voltage in the prior art. This has repercussions on the measurement device. If it were desired to keep the same measurement device, then, to keep the insulation, each of the dimensions would also need to be increased by a factor of two. The volume of the measurement device would then be increased eightfold. This would then raise many problems. One of these problems is related to the space requirement of the measurement device that would become incompatible with the manufacture of a compact apparatus, especially in the case of a mobile apparatus.
U.S. Pat. No. 5,818,706 discloses a high-voltage generator can be obtained by the serial association of several voltage rectifier stages. In order to measure the high voltage produced, a bleeder is parallel connected to the series of rectifiers. The bleeder has as many resistors as it has rectifier stages. Each resistor of the bleeder is associated with a rectifier stage. Each resistor also has an associated shielding cover, this shielding cover being connected to a potential existing at the output of the rectifier stage with which the resistor is associated. The device of U.S. Pat. No. 5,818,706 has several drawbacks as a result of the shielding, including space requirement, metal for the shielding giving rise to electrical arcing, and parasitic capacitances.